Lubricating oil



Patented Mar. 4, 1941 1 rreo LUBRICA'EING OIL No Drawing. Application .ianuary 28, 1939,

Serial No. 253,282

11 Claims.

This invention relates to petroleum lubricating oils and, more particularly, to improved petroleum lubricating oils highly resistant to the formation of sludge. The invention includes 55 certain novel addition agents capable of imparting to petroleum lubricating oilsa high resistance to sludge formation and also includes compounded lubricating oils containing these novel addition agents.

Petroleum lubricating oils have a tendency to form sludge, this tendency depending to a substantial extent upon the source of the oil and the extent'to which it has been refined. The sludge is generally formed as a result of oxidation of the oil and the oxidation is promoted by aeration and high temperature, the greater the aeration and the higher the temperature to which the oil is subjected the more sludge is produced.'

Petroleum lubricating oils used in internal and high temperatures. The modern trend in design and operation of internal combustion engines with an aim toward more power and greater speed have imposed upon lubricating oils a heavy 25 burden in the form of greater aeration and higher operating temperatures than heretofore encountered. In the absence of some agent which retards the normal sludge formation in a lubricating oil for an internal combustion engine the sludge produced during use of the oil accumulates in the oil circulation lines and pump and decreases the effectiveness of the lubricating system. The sludge further deposits on and adjacent the piston rings of an engine, first caus- 35 ing the piston action to become sluggish and finally causing the rings to stick within the ring grooves of the pistons. A further concomitant of sludge formation is an increase in the viscosity of the oil which, in turn, decreases the effective- 4 ness of the oil as a lubricant.

It has been proposed heretofore to incorporate in; petroleum lubricating oils various addition agents which have the property of increasing the resistance of such" oils to sludge formation. These addition agents retard sludge formation in several different ways. Some agents break the oxidation chain of the oil by reacting with some of the intermediate products formed during this oxidation and thus prevent the ultimate forma- 50 tion of sludge. Other agents disperse the sludge as it is formed so that oxidation is not retarded but the effect of the oxidation, insofar as sludge is concerned, is concealed.

The effectiveness of the known addition agents 55 which retard sludge formation is usually measured by an oxidation test during which the compounded} oil containing the addition agent is subjected to aeration at an elevated temperature. The temperature at which such tests are conducted is in the neighborhood of that tem- 5 perature encountered in the crank-case of an internal combustion engine but this temperature is below that which is encountered on the piston rings of the engine. Thus, many addition agents which appear during oxidation tests to be valuable anti-sludging agents are actually of no value in preventingsludge formation on piston rings of internal combustion engines where operating temperatures in the neighborhood of 500 F. are commonly encountered. Moreover, most of the anti-sludging agents heretofore proposed are incompatible with other addition agents which often must be added to lubricating oils to impart film strength and other desirable features to an oil deficient in these qualities, and this incompatibility is a serious limitation to the value of such anti-sludging agents. After extensive investigation, we have found that secondary dialphylamines in which each alphyl group contains at least ten carbon atoms retard sludge formation in petroleum lubricating oils to a remarkable extent. These dialphylamines may be represented by the formula R-NHR where R and R are alphyl radicals,

these radicals containing either the same or a different number of carbon atoms. By alphyl radicalswe mean open chain aliphatic hydrocarbon radicals. We have found that amounts of these dialphylamines ranging from about 2% to about 6% may be incorporated in petroleum lubricating oils with particular advantage, the actual amount used being controlled to a major extent by the type of oil in which the dialphylamines are incorporated and by the severity of the use to which the oil is to be subjected. to

These addition agents are stable not only under storage conditions but also at the high temproperties of lubricating oils and the presence of these other addition agents does not impair the effectiveness of the dialphylamines.

The dialphylamines which we have found to be particularly eifective are the amines derived from naturally occurring alphyl acids all of which have an even number of carbon atoms. The alphyl groups in a dialphylamine may, within the scope of our invention; contain different numbers of carbon atoms with at least one of the alphyl groups containing from 10 to 22 carbon atoms. We have found, furthermore, that the effectiveness of the dialphylamines appears to increase with the number of carbon atoms in the chains of the alphyl group, this increased efiiciency 'being more pronounced between dialphylamines having a relatively small number (10-16) carbon atoms. The solubility of the dialphylamines in petroleum lubricating oils appears to decrease in this same order beginning, at least, with alphyl groups containing 14 carbon atoms. For example, we have discovered that didecyl amine (10 carbon atoms in each alphyl group) is highly soluble and'that it is a mildly effective antisludging agent particularly useful where the oil in which it is incorporated is not subjected to severe operating conditions. Dilauryl amine (12 carbon atomsin each alphyl group) is not only highly soluble in lubricating oils but is particularly effective in preventing sludge formation in lubricating oils which are subjected to severe operating conditions. Dimyristyl amine (14 carbon atoms in each alphyl group) and dioctadecyl amine (18 carbon atoms in each alphyl group) are also highly effective anti-sludging agents although they are progressively less soluble in most lubricating oils. pletely soluble to the extent of at least 3% in a lubricating oil at a temperature of about F. whereas dioctadecyl amine is soluble in the oil to the extent of 3% only at a temperature in the neighborhood of 150 F. Didocosyl amine (22 carbon atoms in each alphyl group) may also be used although the lubricating oil in which it is incorporated must be kept at an elevated temperature to insure solubility to the extent of 3% by weight of the amine in the oil.

The dialphylamines used in accordance with our invention may be prepared by treating the corresponding alphyl (aliphatic) acid with ammonia to produce the alphyl-nitrile and subsequently reducing the nitrile with hydrogen and the aid of a nickel catalyst to produce a mixture of primary secondary and tertiary alphylamines. The secondary alphylamine may be separated from the primary and tertiary amines by fractional distillation to, obtain a product predominantly containing the secondary alphylamine.

The foregoing method may be used with only slight modification in the preparation of each of the dialphylamines referred to hereinbefore.

The following procedure will fully describe the At the end of this time the temperature of the material in the still was raised until distillation of the nitrile occurred.- The distillate was col lected in narrow temperature ranges. In all, 25.1

parts by weight of distillednitrilewere collected.

Dimyristyl amine is com- These fractions were then redistilled cutting out a fraction between 373 and 403 F. at mm. pressure, consisting predominantly of laurylnitrile, The theoretical boiling point of this nitrile is 388 F. at 100 mm. pressure. The laurylnitrile fraction recovered comprised 11.6 parts by weight. The acid number of this laurylnitrile was 0.65 whereas the theoretical acid number for pure laurylnitrile is 0.0, and the nitrogencontent of this nitrile was 7.38% determined by the Kjeldahl method, whereas the theoretical nitrogen content for pure laurylnitrile is 7.72%.

The nickel catalyst used in the subsequent reduction of the laurylnitrile was prepared by charging nickelic oxide to a pressure chamber with an excess of hydrogen and carrying on reduction of the oxide for a period of six hours at a maximum temperature of 510 F, The resulting mixture of metallic nickel and nickel oxide is an active catalyst for the reduction ofthe nitriles to amines.

Dilaurylamine was then prepared by charging 4654 parts by Weight of the laurylnitrile to a pressure chamber with about 128 parts by weight of hydrogen and a mixture of metallic nickel and nickel oxide resulting from reduction of 893 parts by weight of nickelic oxide. This quantity of hydrogen was about 25% in excess of that required theoretically to reduce the nitrile and the quantity of oxide from which the nickel catalyst was prepared was equivalent to 630 parts of metallic nickel or 1/7.3 of the laurylnitrile charged to the pressure chamber. The mixture of laurylnitrile and hydrogen was heated to about 500 to 520 F. for a period of one and one-half hours. The reaction product was then cooled, filtered from the catalyst, and fractionated to yield a product boiling within the range of 420 to 450 F. at 2 mm. pressure and consisting predominantly of dilaurylamine. The yield of this product was about 26% of the final reaction products and had a melting point of about to F. An analysis of the nitrogen content of this fraction by the Kjeldahl method, which indicates only about 80% to 85% of the nitrogen actually present, gave a value of 3.44% which compares favorably with the theoretical nitrogen content of 3.96% for pure dilaurylamine. We believe at this time that this product which we refer to herein as dilaurylamine contains a minor proportion of primary and tertiary laurylamines and may also contain small amounts of amines formed by various combination and permutations of caprinitrile (C10) and myristyllnitrile (C14) included within the laurylnitrile fraction which was used in the preparation of the dilaurylamine. It must be emphasized, however, that our invention is not limited to the use of dilaurylamine prepared in accordance with the foregoing procedure but is drawn to the use of dilaurylamine and other dialphylamines, and combinations thereof, of acceptable purity regardless of the source or method of preparation.

Special methods have been devised for determining the rate of sludge-formation in various oils and under various temperature conditions. A generally satisfactory method has been described in the S. A. E. Journal, vol. 34, page 167 (1934), whereb the time is determined in which 10 mg. of sludge is formed in 10 g. of the oil maintained at a temperature of 341 F. while air is bubbled through the oil at a specified rate. This time is designated the sludging time and is a relative measure of the rate of sludge-formation in that particular oil under the particular conditions of the test. The time required to form this amount of sludge is designated hereinafter as the sludging time for the formation .of 0.1% tar (or sludge). The time required to form 1.0% tar is that required to form 100 mg. of sludge in 10 g. of oil under the conditionsof the foregoing test method.

We have incorporated varying quantities of dilaurylamine in a petroleum lubricating oil having an A. P. I. gravity of 20.9, a flash point of 375 F., a viscosity of 514 seconds Saybolt Universal at 100 F., aviscosity of 54.5 seconds Saybolt Universal at 210 F., a viscosity index of 25.8 and a pour point of 10 F. The sludging time for this lubricatin oil alone was 14.5 hours fOr 0.1% tar formation and 41.0 hours for 1.0%,

tar formation. The sludging time for this same oil in which 3.0% dilaurylamine had been incorported was 33.0 hours for 0.1% tar formation and 49.0 hours for 1.0% tar formation. The sludging time was increased to 40.0 hours for 0.1% tar formation and 63.3 hours for 1.0% tar formation by incorporating 5.0% by weight of dilaurylamine in this base oil. These tests show that the sludging time of the base oil is markedly increased by the addition of dilaurylamine and that the sludging time is increased by increasing the amount of dilaurylamine' incorported in the oil.

In.view of the fact that the sludging time is not an absolute criterion for the efiectiveness of an .anti-sludging agent, we carried out tests on a one cylinder Caterpillar Diesel engine with a base oil similar to that used for the sludgingtime tests and also with this base oil in which dilaurylamine had been incorporated. The base oil had an A. P. I. gravity of 205, a flash.point of 385? F., a viscosity of 499 seconds Saybolt Universal at 100 F., a viscosity of 53.4 seconds Saybolt Universal at 210 F., a viscosity index of 17.8, and a pour point of 10 F. These tests were conducted in accordance with the standard Caterpillar #1 test procedure comprising a 6 hr. break-inperiod with operation continued to 100 hours at 850 R. P. M. and 75 lbs. per square inch brake mean effective pressure at a power output of 16.7 B. H. P. The base oil alone produced heavy carbon deposits on the compression rings, a gummy deposit upon the oil rings and piston, and resulted in a considerable wearloss in the rings and liner. The same test conducted with the base oil in which 3.0% by weight of dilaurylamine and 1.0% tricresyl phosphate, as a film strength agent, had been incorporated deposited no carbon on the compression rings during the 100 hr. test, left the oil rings free from any gummy deposit, and left the piston skirts metal-clean. The average ring wear for the 100 hr. test using this compounded oil was a loss of 0.00017 in. and the average wear of the liner was a loss of 0.0020 in. computed for 1,000 hours on the basis of a 100 hr. test. These wear losses are remarkably low.

The foregoing tests were carried out .using dilaurylamine prepared ,as described hereinbefore. We have also conducted tests on other dialphylamines and have found that 3% of didecylamine in a lubricating oil inhibits sludge fortion agents are incorporated in order to insure complete solubility of 3% by weight of these agents in the oil. Didocosylamine is also effective as a sludge inhibitor but is difiicultly soluble in most lubricating oils. The addition agents of our invention may be used with advantage in a wide range of petroleum lubricating oils of different sources and are not limited to use with the. particular lubricatingoil referred to in the foregoing examples. The dialphylamines increase the resistance of an oil to sludge formation with increase in the quantity of the amines incorporated in the oil up to the limit of their solubility in the oil. Furthermore, the addition agents of our invention are'compatible with other addition agents which may be added to the compounded oil to improve its characteristics in other respects. For example, film strength agents such as phenyl stearic acid and tri-cresylphosphate may be incorporated with the usual satisfactory results in a compounded lubricating oil containing dialphylamines without afiecting the anti-sludging efiectiveness of the dialphylamines and with'the production of a lubricating oil which not only resists sludge formation but which also has excellent wear and lubricating properties. These dialphylamines are also compatible with known pour point depressors as well as with corrosion inhibitors, such for example, as

dilaurylphenol disulphide, so that the presence of such pour depressors and corrosion inhibitors has no efiect upon the efiiciency of the dialphylamines as inhibitors of sludge formation. The fact that dialphylamines are compatible, with known film strength, pour-point depressing, and corrosion-inhibiting agents is of utmost importance in that these sludge inhibitors of our invention may be used with particular advantage with other addition agents in order to produce a petroleum lubricating oil vpreemin'ently suitable for the lubrication of internal combustion engines under any and all operating conditions.

We claim:

1. An improved lubricating oil which comprises a petroleum lubricating oil containing about 2% to about 6% of a dialphylamine having at least ten carbon atoms in at least one of the alphyl groups.

2. An improved lubricating oil which comprises a petroleum lubricating oil containing a dialphylamine having at least 10 carbon atoms in each alphyl group in amount sufiicient to retard sludge formation in the oil.

3. An improved lubricating oil which comprises a petroleum lubricating oil containing a dialphylamine having between 12 to 18 carbon atoms in each alphyl group in amount sufflcient to retard sludge formation in the oil.

4. An improved lubricating oil which comprises a petroleum lubricating oil containing dilaurylamine in amount sufiicient to retard sludge formation in the oil.

5. An improved lubricating oil which comprises a petroleum lubricating oil containing from about 2% to about 6% of dilaurylamine by weight of the oil.

6. An improved lubricating oil which comprises a petroleum lubricating oil containing a mixture of dialphylamines at least one of which has at least ten carbon atoms in each alphyl group said mixture being present in amount suflicient to retard sludge formation in the oil.

7. An improved lubricating oil which comprises a petroleum lubricating oil containing'a dialphylamine having at least ten carbon atoms in each alphyl group and also containing at least one additional compound capable of improving the lubricating properties of the oil, the dialphylamine being present in amount suilicient to retard sludge formation in the oil.

8. A sludge inhibitor for petroleum lubricating oils which comprises a mixture of dialphylamines at least one of which has at least ten carbon atoms in each alphyl group.

9. A sludge inhibitor for petroleum lubricating oils which comprises a secondary alphylamine having at least ten carbon atoms in each alphyl group and containing a minor proportion of primary and tertiary alphylamines.

10. A sludge inhibitor for petroleum lubricating oils which comprises dilaurylamine together with a minor proportion of at least one compound of the group consisting of laurylamine and trilaurylamine.

11. An improved lubricating oil which comprises a petroleum lubricating oil containing a dialphylamine having at least ten carbon atoms in at least one of the alphyl groups in amount sufficient to retard sludge formation in the oil.

JOHN W. FIE'I'ER. FRANKLIN M. WATKINS. 

